0a037dc34719826e667970a3f7dc99140cc4eef6
kate
  Wed Sep 26 10:49:12 2018 -0700
Fix pack mode on cross-chrom item. refs #21917

diff --git src/hg/hgTracks/interactTrack.c src/hg/hgTracks/interactTrack.c
index fdd3f6b..c39f275 100644
--- src/hg/hgTracks/interactTrack.c
+++ src/hg/hgTracks/interactTrack.c
@@ -715,31 +715,31 @@
     {
     struct simpleFeature *sf;
     int shortHeight = tg->heightPer/2;
     for (sf = lf->components;  sf; sf = sf->next)
         {
         if (sf->start > lf->tallStart && sf->end < lf->tallEnd)
             {
             drawScaledBox(hvg, sf->start, sf->end, scale, xOff, y + shortHeight/2,
                                 shortHeight, MG_WHITE);
             }
         }
     }
 else
     {
     struct simpleFeature *sf1 = lf->components, *sf2 = sf1->next;
-    if (sf2->start < sf1->end)
+    if (sf2 && sf2->start < sf1->end)
         {
         drawScaledBox(hvg, sf2->start, sf2->end, scale, xOff, y, tg->heightPer, MG_WHITE);
         }
     }
 }
 
 void interactDrawItems(struct track *tg, int seqStart, int seqEnd,
         struct hvGfx *hvg, int xOff, int yOff, int width, 
         MgFont *font, Color color, enum trackVisibility vis)
 /* Draw a list of interact structures. */
 {
 struct interactTrackInfo *tInfo = (struct interactTrackInfo *)tg->customPt;
 if (tInfo->mergeMode || isLinkedFeaturesMode(tg))
     {
     tg->drawItemAt = interactLinkedFeaturesDrawAt;